Most pipelines that carry fluids need to be “pigged” at certain times. This is accomplished by inserting a pig into the pipeline at a first point and allowing the fluids flowing through the pipeline to push the pig through the pipeline to a second point where it is caught and removed from the pipeline.
Normally, pipeline pigs fall into two basic categories, non-intelligent pigs and intelligent pigs. Non intelligent pigs are those that perform a maintenance or operational function, e.g. cleaning,—such as scraping of solids from the interior of the pipe; swabbing—such as removing liquids or gases from the pipeline; batching—such as separating different fluids in the pipeline, etc. Intelligent pigs are those that monitor and convey information about a particular condition or performance of the pipeline.
Brushes, particularly metal brushes, may be used in various pipeline applications.
For example, Magnetic Flux Leakage (MFL) is an in-line inspection method used to evaluate and monitor metal loss in pipelines, which can result for example from corrosion of pipelines.
Metal brushes are used in MFL tools as part of a magnetizing system that is used to magnetize the pipe that is being inspected. The ends of the metal brushes rub against the wall of the pipe and transmit the magnetic field to the measuring instrument. The data around a defective section in a pipeline is then interpreted to provide a quantitative analysis on the amount of damage.
As another example, brushes, including metal brushes, may be used as cleaning brushes in pipeline cleaning applications. Cleaning pigs, which are known in the art, are used in a number of different applications, for example for regular maintenance of pipelines or to remove heavy deposit and buildup, as by scraping.
Metal brushes have previously been produced by bonding steel bristles to a ferrule or other support by use of solder. However, the use of solder to bond the bristles to each other and to the ferrule or other support presents problems, and is not ideal. As it is not ferrous, it is somewhat insulating and therefore is less conductive than desired for some applications. The process of soldering uses flux, which causes corrosion and which also can affect the magnetic properties of the brush. Solder is a malleable material and has inferior retention properties, causing the bristles to tend to become detached from the solder, and therefore the brush. To effectively solder bristles into a ferrule or other support, heat is used, and depending upon the amount and duration of heat, the physical properties of the bristles can be altered (e.g., tensile strength). Finally, to effectively solder bristles into a ferrule or other support, the bristles usually have to be treated or coated with a material such as tin or nickel, which smoothes the surface of the bristles and allows the molten solder to wick up the support and between the bristles.
In order to avoid some of the problems associated with the use of solder, the inventors have used welding instead of soldering to hold a bristle bundle into a ferrule or other support. While welding has some definite advantages over soldering, welding is expensive in terms of capital and/or labor costs, it is labor intensive (as is soldering), it requires the use of heat and therefore in some instances will negatively affect the properties of the bristles (hardness, brittleness), and the weld metal differs in conductivity from the bristles, which may be problematic in some applications.
What is needed is a less labor-intensive process than soldering or welding that can be used to securely hold a bristle bundle in a metal support, for use in pipeline applications. Preferably, this process would avoid the use of heat, and would be less costly while providing as good as or better retention, than soldering or welding.